Mechanisms Shaping Intra-species Interactions in Streptococcus pneumoniae

• Autor(a) principal: Baía, Inês Sofia Lima
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/131998
• topic: Streptococcus pneumoniae; intra-species interactions; biofilms; amensalism; commensalism; bacteriocins; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

Streptococcus pneumoniae, pneumococcus, is a frequent asymptomatic colonizer of the human upper respiratory tract. Although infrequently, pneumococci can reach other body sites and cause diseases. These are associated with high morbidity and mortality worldwide. Co-colonization by more than one pneumococcal strain occurs and interactions can be established between strains. These interactions may be important to shape the pneumococcal population and how it evolves. Although the mechanisms underlying these interactions are poorly studied, they are important to understand vaccine impact and colonization dynamics. A previous study from the group identified interactions occurring between pneumococcal strains grown in an in vitro biofilm model. Two strong interactions were identified: i) an amensalism interaction in which strain 1990-19F inhibited strain 7031-NT’s growth; and ii) a commensalism interaction in which strain 5435-NT benefited when in co-culture with strain 7632-15A. The aim of this thesis was to identify the molecular mechanisms underlying these specific interactions. Experiments were conducted using variants of each strain labelled with green or red fluorescent protein (GFP or RFP, respectively) which enabled cell counts and strain discrimination by flow cytometry in experiments using mixed cultures. The amensalism interaction was also detectable in planktonic cultures. The interaction was shown to be mediated by a secreted protein and possibly other factors. Competence-induced fratricide (a competitive mechanism mediated by protein effectors), medium acidification and differences in the growth patterns of strains did not seem to play a determinant role in the interaction. The commensalism interaction was inconsistent in planktonic growth and, in a transwell experiment, this interaction was shown to be cell contact dependent. The 15A capsule itself was suggested to be important for the beneficial effect observed on the NT strain. In conclusion, this work provided new insights into the factors that may mediate amensalism and commensalism interactions between pneumococcal strains.